In the design of aircraft, it is desirable to operate the aircraft accessories with a constant frequency source of electric power. In some conventional systems, an integrated drive generator is used, powered by the aircraft engine. The generator or alternator provided for this purpose must therefore be driven at a constant speed. As aircraft engines usually have a wide speed range to accommodate the varying power requirements of take-off, landing and flight, a constant speed drive transmission driven by the engine and driving the generator or alternator at a constant speed must be provided to maintain a stable source of electric power for the aircraft's electrical accessories Various parameters are considered in designing such a constant speed transmission, such as the confined envelope or space into which the constant speed transmission is mounted between the engine and the generator or alternator, and the transmission must be capable of delivering considerable power to the alternator under varying environmental conditions and over a wide range of input speeds. Examples of such integrated drive generators are shown in U.S. Pat. Nos. 3,365,981 to Gantzer, dated Jan. 30, 1968, and 4,252,035 to Cordner et al, dated Feb. 24, 1981, both assigned to the assignee of the instant invention.
Such integrated drive generators as described above include a casing with an input shaft extending into the casing to drive the components of the generator. Coolant or oil is used for cooling and lubricating the various components of the drive and generator. Oils commonly used in such applications are hydroscopic, i.e. tend to take on water. Therefore, one of the problems encountered with such systems is that the oil tends to take on or absorb moisture or water during storage externally of the unit or during operation. This is caused by a combination of various factors, such as temperature changes, speed changes, variable loads and the like. This condition is more prominent during high temperature, high humidity conditions. The moisture and other insoluble compounds become entrained in the circulating air/oil mixture which lubricates and cools the integrated drive generator. When the air increases in temperature, the air itself is capable of containing more moisture or water. Consequently, it has become desirable to purge the system, i.e. exchanging the air with dry air periodically during operation. For instance, the air volume may be exchanged every hour.
To further facilitate an understanding of these problems, it should be understood that a lubricating/coolant oil is manufactured by combining an organic acid with an alcohol which combines to form an ester (oil base) plus water. The water is driven off during the manufacturing process of the oil. However, during operation of such electromotive means as integrated drive generators, as described above, as water is taken on or absorbed in the air/oil composition which lubricates and cools the integrated drive generator, the reaction reverses itself and acids again are formed. These acids corrode the casing and other components of an integrated drive generator. Therefore, as temperatures increase on newer and newer applications, the oil becomes increasingly susceptible to water vapor degradation if the vapor cannot be removed.
This invention is directed to solving the above problems by providing a new and improved, simplified and self-contained liquid vapor purging system.